An antifungal (used with amphotericin)
Flucytosine
A hospital antifungal used together with amphotericin for serious infections such as cryptococcal meningitis.
What is Flucytosine?
Flucytosine is an antifungal used in hospital, almost always together with amphotericin, to treat serious fungal infections such as cryptococcal meningitis and severe candida infections. Using the two together makes the treatment more effective than either alone. The main things to watch for are effects on the blood counts, which can be suppressed, so blood is checked regularly, and blood levels of the medicine itself are also measured to keep it in a safe range. It is always given and monitored by specialists.
Education and reference only. This is a plain-language guide to Flucytosine — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Flucytosine is an antifungal used in hospital for serious, deep-seated fungal infections, most often cryptococcal meningitis (a fungal infection around the brain) and severe candida infections. It is almost always combined with amphotericin rather than used on its own, because the fungus can become resistant if flucytosine is used alone. It can be given as a drip into a vein or, in some cases, by mouth, but always under specialist care.
How it works
Flucytosine is taken up by the fungal cells and turned inside them into a substance that disrupts the fungus's ability to make the building blocks it needs to grow and repair itself. This stops the fungus multiplying. It works particularly well alongside amphotericin, which damages the fungal membrane and helps flucytosine get inside the cells, so the two together are more effective and help reduce the chance of resistance developing.
Company & origin
Originated / developed by: Generic (originally Meda/Mylan).
An antifungal used in hospital, usually together with amphotericin, for serious fungal infections such as cryptococcal meningitis.
Practical use
How to take Flucytosine
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given in hospital, usually as a drip into a vein and sometimes by mouth, alongside amphotericin.
- The specialist team sets and adjusts your treatment, including in people with kidney problems.
- Blood tests check your blood counts and the level of the medicine in your blood, so attend these as arranged.
- Tell the staff if you notice unusual bruising, bleeding, sore throat or fever, which can be signs of low blood counts.
- Keep taking your other prescribed medicines as advised, as it is used alongside treatment of your main illness.
Weighing it up
Advantages & disadvantages of Flucytosine
Advantages
- Works well in combination with amphotericin for serious infections such as cryptococcal meningitis.
- Penetrates well into difficult sites, including the fluid around the brain.
- Blood levels can be measured, helping keep treatment both effective and safe.
Disadvantages
- Can suppress the bone marrow and lower blood counts, so regular blood tests are needed.
- Should not be used on its own, as resistance can develop quickly.
- Needs dose adjustment and careful monitoring in people with kidney problems.
Practical use
Good to know
Flucytosine is a specialist hospital medicine and is used together with amphotericin rather than alone. The main caution is that it can suppress the bone marrow, lowering blood counts, so blood is checked regularly during treatment. To keep it both effective and safe, the team measures the level of the medicine in the blood and adjusts treatment to keep it in the right range, since too much increases the risk of blood and liver effects. The dose is reduced in people with kidney problems, because the medicine is removed by the kidneys. It is given alongside treatment of the underlying illness.
Who should not take it / use with caution
- People who have had a serious reaction to flucytosine should not be given it.
- It is used with great caution, and the dose reduced, in people with kidney problems or existing low blood counts.
- In pregnancy it is generally avoided unless a severe infection makes the benefit outweigh the risk.
Monitoring
- Regular blood counts during treatment.
- Blood levels of flucytosine to keep it in a safe and effective range.
- Kidney and liver blood tests, with dose adjusted for kidney function.
Side effects
- Nausea, vomiting and diarrhoea.
- Lowered blood counts (affecting white cells, red cells or platelets), checked with blood tests.
- Changes in liver blood tests, and rarely more serious blood or liver effects.
Key interactions
- It is used together with amphotericin, which can reduce kidney function and so raise flucytosine levels in the blood; because higher levels increase the risk of bone-marrow suppression, blood counts and flucytosine levels are watched especially closely when the two are combined.
- Other medicines that lower blood counts can add to the risk, so the team monitors closely.
- The specialist team reviews all your medicines and your kidney function during treatment.
Available as: A drip (infusion) into a vein, and sometimes tablets by mouth, given in hospital.
Answers
Flucytosine: frequently asked questions
Why is flucytosine given with amphotericin?
The two work better together than either alone, and combining them helps stop the fungus becoming resistant, which can happen quickly if flucytosine is used by itself.
What is it mainly used for?
It is used for serious fungal infections, especially cryptococcal meningitis (a fungal infection around the brain) and severe candida infections.
Why are my blood counts checked so often?
Flucytosine can suppress the bone marrow and lower blood counts, so regular blood tests let the team pick up and manage this early.
Why is the level of the medicine measured?
Measuring the blood level helps keep the dose effective while avoiding too much, which would raise the risk of blood and liver effects.
Does kidney function matter with this medicine?
Yes. It is removed by the kidneys, so the dose is reduced and monitored carefully in people with kidney problems.
The wider class
About Antifungal (used with amphotericin)
Flucytosine belongs to the antifungal (used with amphotericin) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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